The bovine leukosis virus

Abstract

Lymphocytic leukosis of cattle is characterized by neoplasia of lymphoid tissue; an increased lymphocyte count, i.e., a persistent lymphocytosis is common, but not a constant feature. There are four forms of bovine leukosis distinctly classified by epizootiologieal, clinical, and patho-anatomical criteria. Sporadic bovine leukosis comprising the calf form and the thymic form, as well as cutaneous leukosis, have a low incidence. In the enzootic form, mainly affecting cattle three or more years old, scattered lymph nodes are enlarged and often the heart, abomasum and uterus are affected. The disease occurs as multiple cases within a herd. Enzootic bovine leukosis is the most important neoplastic disease in cattle and its occurrence and economic losses have been described throughout the world. In the Federal Republic of Germany, enzootic bovine leukosis occurs predominantly in Frisian cattle and to give an impression about the incidences some figures from the State of Lower-Saxony are mentioned [10]. In 1975, the blood from cattle of 87,095 herds was examined for persistent lymphocytosis, i.e. 84.3% of all herds in the State. In 4,238 of these herds, i.e. 4.9%, animals with persistent lymphocytosis were detected, and 12,455 leukotic animals had to be slaughtered. With regard to the etiology of the disease, epizootiologic and transmission studies performed in the past gave suggestive evidence for an infectious agent likely to be transmitted both horizontally and vertically without entering the germ line. But, not before Miller et al. [8] described type C particles in short-term lymphocyte cultures derived from leukotic cows, was an association between type C particles and bovine leukosis firmly based on experimental data. However, these lymphocyte cultures were not well suited for the characterization of the bovine C type particles, and, therefore, it was a great breakthrough when Van der Maaten et al. [ 11 ] were successful in establishing long-term cultures which continued to release adequate numbers of bovine C type particles for which, by transmission experiments, suggestive evidence was given that they represent the bovine leukosis virus (BLV).